For semiconductor device production units requiring super-clean conditions, corrosive gases such as chlorine based gas, fluorine based gas and the like are used as a depositing gas, an etching gas, and a cleaning gas. Therefore, if a conventional heater wherein the surface of a resistance heating element is covered with a metal, such as stainless steel or Inconel, is used as a heater to heat wafers which are exposed to the corrosive gas, unfavorable minute chloride, oxide, fluoride, and other particles with diameters of a few .mu.m are formed due to the exposure of that metal to the corrosive gas.
In view of this, with those etchers and CVD units running at low temperatures, as illustrated in FIG. 1, by way of example, an arrangement used to be adopted, wherein infrared lamps 5 are installed outside a chamber 1 via a quartz window 4, the chamber interior being exposed to deposition-gas, etc.; a susceptor 2 made of aluminum for example is installed within the chamber 1 through an arm 3; and the susceptor 2 is heated by the infrared lamps 5, whereby a wafer W placed on the susceptor 2 is indirectly heated. In this arrangement, the metal susceptor 2 is used as an electrode for plasma generation, plasma is generated within the chamber 1 with high-frequency electric energy fed directly to susceptor 2 so as to form a semiconductor film on the wafer W and clean it. In this case, the aluminum susceptor 2 has an insulating film of alumina with a thickness of approximately 10 .mu.m formed over its surface through an anodized aluminum production process so that wafer W was placed on this insulating film might be prevented from against directly receiving high-frequency electric energy. High-frequency electric energy discharging takes place with this insulating film maintained charged at a certain level within the plasma, since no charges flow to either one electrode, unlike current discharging.
However, in the above-mentioned conventional case the susceptor 2 was made of a metal, and therefore wafers were unfavorably contaminated with a heavy metal. Particularly, the aluminum susceptor 2 was confronted with a problem of Mg-contamination. To solve the problem of such contamination, it has been proposed that susceptor 2 be insulating and a plate-like electrode 6 be attached to the rear face of the susceptor for plasma generation, as illustrated in FIG. 2 by way of example. Regrettably however, a further problem occurred wherein the plate-like electrode 6 for high-frequency electric energy supply intercepted infrared rays from infrared lamps 5, and the heating capacity of the susceptor 2 further declined. In addition, with said susceptor, the point of plasma generation deviated from the set position of the wafer W, whereby preferable plasma generation was generated, resulting in decreasing wafer cleanability. The susceptor with a ring-like electrode fitted around the outer periphery thereof also caused a similar problem.
Although said insulating film remains charged at a certain level in the stage of plasma generation for such processes as physical vapor deposition (PVD process), chemical vapor deposition (CVD process) or in an etching unit, electrolytically dissociated ions and electrons collide against the charged insulating film to damage said insulating film. Particularly, the anodized aluminum insulating film lacking denseness and having a thickness of approximately 10 .mu.m at most gave a short service life. Especially with the CVD process unit, an etching unit and the like using halogen-based corrosive gas, the anodized aluminum insulating film having such short service life requires frequent replacement. It was discovered that particularly the metals such as aluminum, etc. had undergone heavy corrosion by the plasma of the halogen-based corrosive gas, whereby the susceptors of these metals went through serious deformation to such an extent that the susceptors failed to provide normal service.
The inventors discovered the following problem referred to hereunder in the course of investigations. Namely, in such a process using plasma as referred to above, the molecules of the gas are first dissociated to release highly reactive positive ions and electrons and thereby generate a plasma zone. Since the electrons which electrolytically dissociated at that time each have a smaller mass, they move more rapidly as compared with ions, resulting in producing a region with a smaller electron density near a high-frequency electrode. This region with the smaller electron density is called a plasma sheath. Utilizing the potential of the plasma sheath, the ions within the plasma are accelerated, and the accelerated ions are brought into collision against the wafer surface. Ions of different species are selectively applied respectively for etching, CVD and PVD.
But, in the case with the susceptor of anodized aluminum applied as referred to above, the plasma sheath did not grow stably, sometimes failing to assure stabilized plasma discharge. As a consequence, there sometimes occurred failure of effecting stabilized etching, CVD and PVD over the entire surface areas of the susceptor.
In the semiconductor device production units, an electrostatic chuck is now used for the purpose of the transfer, the exposure to light, film formation, micro-processing, cleaning, dicing, and so on for the wafers. The following are known as an electrostatic chuck:
(1) An electrostatic chuck which is obtained through screen-printing a filmy electrode on a disk-like ceramic green sheet, placing another disk-like ceramic green sheet on the resultant to cover the screen-printed filmy electrode, followed by press-molding, and sintering the resulting ceramic green sheet assembly. Pressing the ceramic green sheet molding inevitably causes non-uniform pressurization, whereby the thickness of a dielectric layer of the electrostatic chuck becomes non-uniform, thus resulting in not only rendering difficult the manufacture of such chucks, but also reducing the yield of production thereof.
(2) To solve this problem, the present inventors developed electrostatic chuck 7, schematically illustrated in FIG. 3. That is, a disk-like dielectric plate 8 of dense and insulating ceramic and a disk-like support 10 of insulating ceramic are prepared. The disk-like support 10 has a through hole 11. Further, a circular sheet of a conductive bonding agent and a columnar terminal 12 are prepared. The circular sheet is held between the disk-like support 10 and the back side of the dielectric plate 8. The columnar terminal 12 is put into through hole 11. In this state, the resulting assembly is thermally treated and thereafter, the dielectric plate 8 and the disk-like support 10 are bonded together, using the conductive bonding agent layer 9. Then, the dielectric plate 8 is polished to flatten a wafer-attracting surface 13.
It is however noted that in the process of (1), the thickness of the dielectric layer is likely to become irregular due to certain restrictions in the production. In this regard, a complementary description is made hereunder. In the method in which the respective green sheets are laminated one upon another after providing the print electrode on one of the green sheets, press-molded and fired, there inevitably is non-uniform thickness of the dielectric layer and poor adhesion of the assembly components at the respective stages of the press-molding and the firing. Namely, these problems coincide with the displacement of the print electrode inside the sintered assembly. In view of this, it is difficult to make uniform the thickness of the dielectric layer no matter how fine the surface of the dielectric layer is planed after the monolithical sintering. In the sintering process under normal pressure, as the assembly size goes up, it is difficult to secure the denseness of the dielectric layer at 100%, and from the standpoint of preventing dielectric breakdown, this sintering process deteriorates its reliability. Moreover, since the electrode is formed by the screen printing process, the electric resistance thereof is relatively large. Accordingly, it is difficult to increase the rise speed for actuating the electrostatic chuck.
Meanwhile, in the process of (2), the disk-like support 10 and the dielectric plate 8 are molded, sintered, and mechanically surface-polished. Particularly with the dielectric plate, it is necessity to plane it to make uniform the thickness. Further, it is required to bond together the disk-like support and the dielectric plate through heating with the circular sheet of silver solder or the like sandwiched therebetween. Therefore, it is necessary to implement the grinding of the disk-like support 10 and the dielectric plate 8, the thickness adjustment thereof, and very troublesome silver-soldering to join together said support 10 and said dielectric plate 8, thus resulting in increasing the number of processing steps, and thereby interfering with efficient mass production. Joining together the disk-like support 10 and the dielectric plate 8 using a conductive bonding agent such as silver solder or the like leaves behind a joint face along the conductive bonding agent layer 9. However, this joint face gives rise to a factor for the dielectric breakdown under high vacuum condition. Further, with regard to these electrostatic chucks, high-frequency wave generating electrodes, etc., it has been clarified that the following problem occurred. Namely, with semiconductor device production units, such a method is generally put into practice, which comprises the-steps of supplying a gas into the unit and applying high-frequency electric power to the gas for the plasma generation. Therefore, said high-frequency wave generating electrodes, and ECR units are finding wide use with the semiconductor device production units for dry etching, chemical vapor-phase growth process, and the like.
Where the ECR unit is employed, the electric power in the form of the high-frequency waves in the microwave band is applied to the gas, whereby ECR locally generates plasma within the high-frequency electric field and also within the static magnetic field with a spatially irregular intensity distribution. Subsequently, a force is applied to the plasma in a certain direction to accelerate the plasma. In the ECR unit, a 2.45 GHz is generally employed as the microwaves. The microwaves are radiated, through an electromagnetic wave permeation window, into the ERC unit, so that plasma is generated in the gas molecules.
As this electromagnetic wave permeation window is exposed to the microwaves having high energy, it is essential for this window to at least release heat due to its heat loss. It is also necessary for the window to have excellent thermal shock resistance so that the window may be difficult to be cracked if it is heated. To meet these requirements, the electromagnetic wave permeation window used to be fabricated of silica glass in the past.
However, the electromagnetic wave permeation windows of silica glass have to date incurred damage by ECR plasma, loss in electromagnetic wave permeability, and breakage. These problems stemmed from the damage of said windows by the plasma.
The inventors attempted to fabricate the electromagnetic wave permeation window of alumina or sapphire, and found that these materials suffered greater dielectric loss compared with quartz, and that the transmission of a microwaves through the alumina or sapphire window entailed a local rise in temperature exceeding 200.degree. C. Generally, it is observed that exposing the electromagnetic wave permeation window to microwaves gives rise to the generation of heat therein due to the inner friction of molecules or polar groups within the dielectric material. Quantity Q of the heat generated is expressed by Q=kfE.sup.2 .epsilon. tan .delta.. In this expression, k is a constant, f a frequency, E an electric field, and .epsilon. a dielectric constant. It was further clarified that as the alumina or sapphire electromagnetic wave permeation window locally underwent intensive heating, such windows of a large diameter over 100 mm failed to resist the thermal impact, and were broken.